基于TCP Vegas与TCP Reno的一种改进拥塞控制算法

因特网的快速发展带来了信息量的急剧膨胀,网络拥塞已经成为制约因特网发展的瓶颈。在众多TCP拥塞控制算法中,TCP Vegas表现出比其他算法更为优越的性能,然而自1995年提出至今,仍然没有取代TCP Reno成为现今最广泛使用的TCP拥塞控制算法。有研究表明,这是由于Vegas在与Reno共存的网络环境下不能公平地竞争到带宽,因此不能实实质性地提高网络性能。本文在分析Vegas与Reno如何在网络路由中占用带宽的基础上,提出一种在两者兼容环境下的拥塞控制方法,根据不同瓶颈缓冲区容量合理选择α、β等参数,实现了在Vegas与Reno共存环境下两者良好的兼容性,并通过仿真实验证明了该算法的有效性和正确性。     

基于TCP NewReno的稳态吞吐量分析模型

最近的研究表明,在当前网络未启用SACK选项的TCP流中,有超过一半的数据流采用TCP New Reno的快速恢复算法.而Padhye提出的基于TCP Reno的TCP吞吐量分析模型,不能准确反映TCP New Reno数据流的吞吐量.Padhye模型在建立过程中采用猝发性丢包模型,同时忽略了快速恢复阶段和超时后的慢启动阶段,影响了预测的准确性.基于此,提出了一种基于TCP New Reno的吞吐量分析模型.在分析过程中,采用了更符合真实网络丢包特征的丢包模型,并且充分考虑了快速恢复阶段和超时后的慢启动阶段对吞吐量的影响.仿真实验表明,该模型可以准确地预测TCP New Reno数据流的吞吐量.     

基于吞吐量和队列检测的TCP Vegas改进算法

TCP Vegas协议通过比较期望吞吐量和实际吞吐量的差值来进行网络拥塞控制,相对TCP Reno协议具有更佳的网络稳定性和利用率。通过分析两种协议在复杂环境中的网络性能,证实TCP Vegas协议在共存环境下公平性欠佳的结论,并提出一种基于网络自适应的TCP Vegas改进算法。该算法通过对期望吞吐量自适应改进和对队列拥塞监测的优化,提高了协议在复杂环境中的自适应性,增强了与TCP Reno协议共存环境下的公平性,最后通过仿真证明了改进算法的有效性。     

基于NS2的无线网络中TCP协议算法性能分析

基于NS2软件仿真,分析有线和无线链路中数据传输的不同点;进一步地在较严重丢包率的情况下比较TCP Reno,TCP Vegas,TCP veno以及TCP westwood拥塞窗口与吞吐量的表现,最后确定TCP westwood算法最适用于无线网络环境.采用这种算法,将提升人们在移动互联网中的用户体验.     

基于认知无线电网络的TCP协议的改进方案

首先搭建认知无线电网络环境,在该网络下分析TCP Reno、TCP Newreno、TCP Sack1、TCP Vegas、TCPWestwood协议的性能包括拥塞窗口、平均吞吐量、丢包率。针对传统TCP拥塞控制在认知无线网络中存在的问题,提出一种跨层优化TCP Westwood的改进算法,称为TCP-CR。该算法区分网络拥塞导致的超时和切换所导致的超时,同时针对不同轻度拥塞进行不同的恢复策略。ns-2仿真结果表明,TCP-CR可以减少TCP的平均慢启动次数,吞吐量比传统的TCP Westwood显著提高。增强了对认知无线网络环境的适应性,从而提高了网络的性能。     

一种改进的TCP拥塞控制算法及仿真

TCP协议提供面向连接、可靠的服务,但应用于时延敏感的实时网络时,并不能保证实时性。当网络负载过大时,会出现拥塞、传输延迟和丢包等问题。为了降低网络拥塞概率,提出了一种改进的TCP拥塞控制算法TCP-EB。该算法根据确认数据包的速率估计网络可用带宽,调整拥塞窗口的大小,提高带宽利用率。出现拥塞时,对窗口衰减速度进行限制,保证传输的优先级高于其他数据流。最后将TCP-EB与传统拥塞控制算法TCP Reno、TCP Vegas进行比较,结果表明,提高了网络吞吐量和网络传输的平滑性。     

基于RTT自适应的无线TCP改进算法

针对TCP Reno在无线环境下的性能恶化问题,在研究分析TCP Reno拥塞控制算法问题的基础上,提出一种基于RTT自适应的改进算法.该算法实现了丢包区分的拥塞窗口与慢启动门限调整,减轻了传统TCP由于无法区分拥塞丢包与误码丢包、盲目将拥塞窗口减半带来的性能下降.分析了该算法的可行性,并通过NS仿真对其吞吐量、带宽利用率、公平性等指标进行评估.仿真结果表明,相对TCP Reno,改进算法实现了无线环境下的TCP性能改善,同时具有一定的友好性与公平性.     

自组网TCP Vegas协议研究

对自组网络内的TCP拥塞控制算法进行了仿真比较研究。主要研究了自组网环境下TCP Vegas拥塞控制算法的性能表现,并尝试对Vegas算法的拥塞避免机制进行改进。改进的主要措施是对拥塞避免阶段网络通信状况进行细致分解,并根据不同的网络状况采取相应的措施;进而提出了Vegas1和Vegas2两种改进方案。与Reno、SACK、Vegas等算法的仿真对比结果表明,无论在TCP吞吐量方面,还是在TCP段的传送效率方面,改进后的Vegas2算法都优于其他算法。     

TCP Veno在MANET环境下的性能研究

将TCP Veno运行在MANET环境下,采用NS2对其性能进行了仿真测试。仿真结果表明：在存在背景流、有随机丢包并且存在拥塞的MANET网络中,TCP Veno的性能优于TCP Reno,而且在背景流越大,达到拥塞的时间越短、随机丢包越大,TCP Veno的优越性更会非常明显。     

基于背景流变化特征的组播拥塞控制算法

大部分组播拥塞控制机制都是将包丢失作为网络拥塞的信号,存在丢包、响应速度慢等缺陷。为了避免这种缺陷,提出一种新的基于背景流变化特征的拥塞控制算法。该方法根据网络队列延迟的变化检测拥塞,使网络能够对拥塞作出快速反应,更有效地利用网络资源,弥补了响应速度慢的缺陷。仿真实验结果表明,在相同的配置下采用该拥塞控制算法的网络,在吞吐量、丢包率等性能上均优于未采用该算法的网络。     

一种基于相对延时的TCP Vegas拥塞避免机制的改进算法

TCP Vegas是一种TCP的实现,在Internet网上能达到令人满意的吞吐量,在通常情况下能较早地发现网络拥塞并成功的防止拥塞丢包。但是它有一个缺陷：当反向链路出现拥塞时,会导致TCP Vegas吞吐量的显著下降。使用“相对延迟”来改进TCP Vegas的拥塞避免机制。当反向链路存在拥塞时,明显提高了TCP Vegas的吞吐量。     

Analysis and enhancement of TCP Vegas congestion control in a mixed TCP Vegas and TCP Reno network scenario

Its more refined congestion control mechanisms, also based on the estimation of round trip delays, allow TCP Vegas to outperform the more widespread TCP Reno congestion control, based only on the packet loss detection, in a number of network environments. However, these mechanisms make TCP Vegas less aggressive with respect to TCP Reno; thereby TCP Vegas sources show high weakness in taking the available bandwidth when competing with other TCP Reno sources. This is a major reason that hinders the spread of TCP Vegas among Internet users. In this work, after a preliminary analytic study about the limits of TCP Vegas in mixed network environments, we describe a new adaptive mechanism for TCP Vegas, called TCP NewVegas, designed in order to improve its performance even in heterogeneous network scenarios. The large number of simulations, presented in this paper, show that TCP NewVegas guarantees good performance even in mixed network environments, without canceling the desirable features (e.g. fairness) that TCP Vegas exhibits in homogeneous environments.     

TCP拥塞控制机制定量性能分析

TCP协议承载着因特网超过70%的传输流量,其拥塞控制机制可以有效地改善网络拥塞现象。剖析了慢启动、拥塞避免、快速重传、快速恢复等拥塞控制机制,研究了Tahoe、Reno、NewReno和SACK等几种常见的TCP拥塞控制算法。借助于网络模拟器NS2对这几种算法的性能进行了定量分析。结果证明：相对于Tahoe、Reno拥塞控制算法而言,NewReno和SACK TCP可以更快、更平滑地摆脱网络拥塞恢复到正常工作状态。     

基于TCP Reno和TCP Vegas拥塞控制性能研究

介绍了传输控制协议(TCP)的拥塞控制技术,对两种典型的TCP拥塞控制算法TCP Reno和TCP Vegas进行了详尽的分析,对其性能进行了比较。同时对TCP Reno和TCP Vegas在混存网络环境下的性能进行分析,并针对TCP Vegas中的和参数进行修改,提出了Vegas-A+算法使它们能并存于网络中。在NS2仿真环境下对改进的控制算法进行了仿真,仿真结果表明了改进算法的有效性。     

基于模糊控制的ad hoc网络TCP算法研究

TCP协议是针对固定可靠网络设计的一种传输协议,它把数据包丢失或延迟的原因都归结为网络拥塞。在移动自组网上直接应用TCP 协议,网络性能会因比特出错率高等原因大幅下降。针对无线自组织网络高误码的基本特征,基于TCP Vegas协议和环回时间的均值和方差改变趋势,采用不同的控制策略调节发送端的数据发送速率,从而优化传输控制协议的吞吐量,提高网络资源的利用率。仿真研究结果表明,与传统的传输控制协议相比,该算法具有更高的吞吐量和稳定的拥塞控制窗口。     

Delay-based TCP congestion avoidance: A network calculus interpretation and performance improvements

In delay-based TCP congestion avoidance mechanisms, a source adjusts its window size to adapt to changes in network conditions as measured through changing queueing delays. Although network calculus (NC) has been used to study window flow control and determine performance bounds, there is a lack of a bridge between NC theory and the practical issues of delay-based TCP congestion avoidance. In this paper, we use an NC-based approach to derive ideal congestion controllers for representative delay-based window flow control models with time-variant feedback delays. We show that the basic delay-based TCP congestion avoidance mechanisms in TCP Vegas, Enhanced TCP Vegas, and FAST TCP can be viewed as different approaches to approximating a certain NC controller. Moreover, we derive another NC controller that is explicitly constructed to address the throughput degradation of the current delay-based methods due to delayed acknowledgement (ACK) packets caused by network traffic in the reverse path (ACK packet) direction. The approximation of this F-model NC-based controller is shown to provide better throughput and fairness over the existing delay-based methods for a variety of network topologies in ns-2 simulations.     

一种有竞争力的自适应Vegas算法

针对TCP Vegas与Reno协议不兼容的问题,提出一种提高Vegas带宽竞争力的算法ACNV,通过估计带宽占有率的变化趋势调节调整源端对带宽资源的抢占力,并采用快速收敛到合理区间的窗口调整策略,达到ACNV与Reno公平分享带宽的目的。实验结果证明,当瓶颈链路带宽由0.1 Mb/s变化到2 Mb/s的过程中时,ACNV与Vegas相比,与Reno共存时平均带宽占有率的平均值从4.3%提高到48.33%。     

Congestion-aware channel assignment for multi-channel wireless mesh networks

In this paper, we propose a distributed congestion-aware channel assignment (DCACA) algorithm for multi-channel wireless mesh networks (MC–WMNs). The frequency channels are assigned according to the congestion measures which indicate the congestion status at each link. Depending on the selected congestion measure (e.g., queueing delay, packet loss probability, and differential backlog), various design objectives can be achieved. Our proposed distributed algorithm is simple to implement as it only requires each node to perform a local search. Unlike most of the previous channel assignment schemes, our proposed algorithm assigns not only the non-overlapped (i.e., orthogonal) frequency channels, but also the partially-overlapped channels. In this regard, we introduce the channel overlapping and mutual interference matrices which model the frequency overlapping among different channels. Simulation results show that in the presence of elastic traffic (e.g., TCP Vegas or TCP Reno) sources, our proposed DCACA algorithm increases the aggregate throughput and also decreases the average packet round-trip compared with the previously proposed Load-Aware channel assignment algorithm. Furthermore, in a congested IEEE 802.11b network setting, compared with the use of three non-overlapped channels, the aggregate network throughput can further be increased by 25% and the average round-trip time can be reduced by more than one half when all the 11 partially-overlapped channels are used.